1. Field of the Invention
The present invention relates to a heating device to heat semiconductor wafers and the like.
2. Description of Related Art
In a semiconductor device manufacturing process, a heating process is performed to form an oxide film and the like on a wafer using a semiconductor manufacturing apparatus. One of heating devices to heat wafers in such a semiconductor manufacturing apparatus includes a resistance heating element embedded in a plate-shaped ceramic substrate having a heating surface on which a wafer as an object to be heated is placed and heated. This ceramic heater is advantageously suitable for not only a film forming apparatus used for the semiconductor manufacturing process but also a surface processing apparatus which performs dry etching for the surface of a plate-shaped material to be heated.
The aforementioned heating device generally includes a substantially cylindrical shaft perpendicularly attached to the joint surface around the center of a surface (joint surface) of the ceramic substrate opposite to the heating surface. The shaft supports the ceramic substrate. Moreover, in internal space of the shaft, a power supply member connected to the resistance heating element embedded in the ceramic substrate and the like are disposed. This shaft is made of a same ceramic as the material of the ceramic substrate. The shaft is produced separately from the ceramic substrate and then fixed to the ceramic substrate by solid-phase bonding or liquid-phase bonding.
The shaft is required to be surely joined to the ceramic substrate with enough strength to support the ceramic substrate so as to ensure airtightness enough to protect the power supply member in the shaft from corrosive gas during heating processing. Furthermore, it is required to keep the joint between the ceramic substrate and shaft good for a long period of time. One of heating devices satisfying such a requirement has a shape satisfying a predetermined relationship between radial length of a ring-shaped joint area where a ceramic substrate and a shaft including a flange portion in a joint end abut on each other and thickness of the flange portion of the shaft (Japanese Patent Laid-open No. 2005-56759).
As a result of improving the shapes of the shaft and joint interface between the ceramic substrate and the shaft in such a manner as disclosed in Patent Literature 1, the requirements for the strength and airtightness at the shaft joint was achieved. However, some products of the heating device improved in such a manner cannot satisfy the required characteristics after the process to join the shaft to the ceramic substrate or accidentally had a problem that the shaft was detached during a heating test, reducing the product yield in some cases.
The present invention is to advantageously solve the aforementioned problems, and an object of the present invention is to provide a heating device which always has high strength at the joint area of the ceramic substrate and shaft and is therefore capable of increasing in product yield.